Rotor assemblies for vehicle alternators are often of a claw-pole type design. These rotor assemblies typically include a pair of annular pole pieces aligned along a longitudinal axis and having bores at their centers. Each of the pole pieces has on its radial periphery a number of axially extending fingers giving that pole piece a claw-like appearance. A coil wire is wound about an annular bobbin forming a bobbin assembly. The bobbin assembly is placed in a region formed between the pole pieces. The pole pieces are mounted on a rotor shaft with the fingers of the respective pole pieces being interleaved with one another. The coil wire, bobbin and pole pieces are coated with a varnish and then baked to hold the coil wires in a fixed position relative to one another.
A slip ring assembly is also mounted on the rotor shaft. The slip ring assembly has a pair of axially spaced slip rings which are adapted to mate with exterior brushes. The slip ring assembly includes a pair of terminals which are connected to respective slip rings. A pair of stamped metal fans is then attached to the axially outboard faces of each pole piece.
The rotor assembly is mounted inside a stator and an alternator housing to form an alternator. When voltage is supplied to the slip ring assembly and the rotor assembly is rotated, the rotor assembly induces the flow of current in the windings of the stator. This current is output from the alternator. Heat generated by current flowing through the coil wire and windings is carried away by air currents, created by the rotation of the fans, through perforations in the alternator housing.
Alternators, constructed as described above, have several shortcomings. First, the high speed rotation of the rotor assembly within the alternator housing creates a significant amount of noise. A portion of this noise is originated by air flowing between the pole pieces and the bobbin assembly during rotor assembly rotation. Likewise, during operation of the alternator, the fingers of the pole pieces may vibrate radially due to forces associated with changing magnetic fields, thereby creating additional noise. An annular support ring, made from a nonmagnetic material, is often placed within the interleaving fingers to provide radial support to the fingers thereby reducing vibration and noise. Also, separate spacer pieces, configured to fit between the interleaving fingers, are sometimes placed between the pieces to reduce air flow disturbance resulting from the nonuniform surface of the rotor.
Second, connections formed between the terminals of the slip ring assembly and the respective ends of the coil wire are subject to failure. The high speed rotation of the rotor assembly, which may be on the order of 18,000-23,000 RPM, subjects the connections to substantial acceleration forces. As these connections are generally isolated from and are not supported by the rest of the rotor assembly, fatigue failures of the connections may occur, with corresponding failure of the entire alternator. Consequently, the alternator must be disassembled, the connections repaired, and the alternator reassembled. Alternatively, the alternator must be completely replaced. In either case, the repair or replacement is expensive and time consuming.
The present invention addresses problems associated with the above-identified shortcomings.